1. Field of the Invention
The present invention relates to apparatus used for installing construction materials in general and to an automatic impact nailing and dimpling apparatus for driving a nail and setting a dimple to a predetermined depth in gypsum wallboard in particular.
2. Description of Prior Art
Gypsum board, also called wallboard and drywall, comprises processed gypsum which is sandwiched between sheets of paper. The board is usually provided in standard sheets 4 feet wide by 8 to 14 feet in length, 1/4 to 1' thickness.
In many applications, such as in the construction of residential wood framed homes, the board is attached to wooden studs by nailing the board to the studs. The nails used typically comprise a cupped head. As each nail is driven through the wallboard and into the stud, it is countersunk in the wallboard. In the process of countersinking the nail in the wallboard, a dimple is formed in the wallboard. The dimples thus formed and butt joints between adjacent boards are then taped and covered with a wallboard compound for providing a smooth uniform surface. Thereafter the surface is painted or covered with a plaster for providing an attractive and aesthetically pleasing appearance.
In the past, the nailing of wallboard to a wooden stud has been done using a conventional wallboard hammer, a single-stroke or reciprocating automatic impact hammer or the like.
In using a wallboard hammer, a nail is hammered into the wallboard and the stud until the base of the head of the nail is flush with the surface of the wallboard. Thereafter, a single stroke of the hammer using the convex surface of the hammer countersinks the nail and at the same time forms a dimple in the wallboard.
A principal disadvantage of the above-described method for installing wallboard is that the head of the nail is struck by the convex surface of the hammer before the convex surface of the hammer contacts the surface of the wallboard. This tends to cause the head of the nail to pierce the paper covering of the wallboard. Also, with hand nailing there is no way to control the depth of the nail set and dimple. The hammer head, therefore, tends to shatter the gypsum core. Also, if the nail is not driven perpendicular to the wallboard, the sharp edge of the head of the nail will tend to pierce the paper covering the wallboard. Once the surface paper covering is pierced, it loses its integrity which reduces the holding ability of the cup headed nail.
Another disadvantage of the above-described method for installing wallboard is that it is time consuming.
Still another disadvantage of the above-described method is that it is difficult to set nails and dimples repeatedly at uniform and preferred depths.
In typical prior known single-stroke and certain reciprocating-type automatic impact nailer and dimpler apparatus, such as disclosed in U.S. Pat. No. 4,610,381 issued to Francis J. Kramer, et al., there is provided a piston member and nail set assembly which is pneumatically driven in a single-stroke or reciprocating fashion, a nail feeding mechanism which automatically feeds nails to a position beneath the nail set, a dimpler having a convex exterior surface with a hole centrally located therein which is activated by the piston member for creating a dimple in the wallboard as the nail is being set, and a triggering mechanism to control the operation of the apparatus.
In operation, the nail is driven through the hole in the dimpler by the piston and when the piston strikes the dimpler, it causes the dimpler to dimple the wallboard.
A principal disadvantage of the above-described single-stroke and reciprocating automatic-type nailing and dimpling apparatus is that, in general, there is no means provided in the apparatus for automatically controlling the depth to which a nail and a dimple is set in the wallboard. As a consequence, if the air pressure in the apparatus varies or the hardness of the wood studs to which the wallboard is nailed varies, the depth to which each of the nails is driven cannot be accurately controlled. This may result in nails not being driven deep enough or driven too deeply. If the nails are not driven deep enough, they will not be properly countersunk and if the dimpler is not driven deep enough, the paper will not be properly dimpled. Alternatively, if the nails and dimpler are driven too deep this can cause the nails and/or the dimpler to tear the surface paper, causing the nails to lose their holding ability.
Another disadvantage of the above-described prior known single-stroke and reciprocating-type automatic nailing and dimpling apparatus is that in such apparatus there is generally no means, such as a sole plate or housing, for insuring that a nail is hammered into the wallboard perpendicular to the wallboard. This often results in a sharp edge of the nail pressing into the paper covering of the wallboard resulting in a greater tendency for the nail to cut through the paper covering of the wallboard as described above.
In applicant's U.S. Pat. No. 4,666,074, issued May 19, 1987, there is disclosed a reciprocating-type automatic impact nailing and dimpling apparatus comprising a sole plate and means for automatically setting a nail or other fastener and a dimple to a predetermined depth in a gypsum wallboard or other substrate. The sole plate insures that the fastener is set perpendicular to the wallboard.
In applicant's patented apparatus there is provided a movable dimpler and a separately movable hammer assembly comprising a movable piston and a nailset which are movably mounted in a housing of the apparatus. Located in a compressed air channel in the apparatus between a source of compressed air, the dimpler and the hammer assembly, there is provided a compressed air control valve. The valve is provided for controlling a flow of compressed air from the source to the dimpler and the hammer assembly including the piston. Extending from the dimpler to the valve is a valve control member for controlling the operation of the valve.
In operation, the apparatus is first connected to a source of compressed air which causes the dimpler and hammer assembly to be automatically retracted into the housing. A nail is then inserted beneath the nailset within the interior of the dimpler over a hole in the dimpler. The sole plate is then placed in contact with a wallboard. The activation of a trigger member then causes the compressed air control valve to be moved to a first position wherein the dimpler and hammer assembly are freed to move and compressed air is channeled to the piston causing the piston to reciprocate and drive the nail through the hole in the dimpler and into the wallboard. Thereafter, the hammer assembly contacts and moves the dimpler. When the dimpler has been moved a predetermined distance relative to the housing, the valve control member extending from the dimpler causes the valve to be moved from its first position to a second position wherein the valve interrupts the flow of compressed air to the piston thereby automatically stopping the reciprocal movement of the piston and further movement of the dimpler into the wallboard. By adjusting the length of the valve control member, the depth of the dimple is controlled. By adjusting the length of the nailset, the depth of the nail relative to the dimple is controlled.